Identifying subterranean structures using amorphous metal markers

ABSTRACT

Disclosed are methods and apparatus for identifying non-metallic subterranean structures using amorphous metal markers associated with the structures. Some examples will include the amorphous metal in the form of one or more sections of an amorphous metal foil within a protective enclosure sufficient to physically isolate the amorphous metal foil from the surrounding Earth. The amorphous metal foil and enclosure may be in the form of a tape which either will be secured to, or placed proximate the subterranean structure, which may be, for example, a pipe or conduit, or other non-metallic structure.

FIELD OF THE INVENTION

The present disclosure relates generally to methods and apparatus foridentifying subterranean structures using amorphous metal markersassociated with the structures; and more specifically relates to methodsand apparatus for establishing location indicators for non-metallicstructures, such as non-metallic pipes or pipelines, tanks, etc. throughuse of amorphous metal markers, such as sections of amorphous metalfoil.

BACKGROUND OF THE INVENTION

A long-standing problem has been that of reliably identifying thelocation of subterranean structures, particularly when the structuresare non-metallic, and therefore do not have a magnetic signature thatcan be detected; these items are also non-conductive and cannot be foundusing conductive or induced current techniques. One common example ofsuch a structure is underground non-metallic conduit, for example suchas PVC or polyethylene pipe or tubing. Although PVC and polyethylenepipe are common structures that need to be identified, similar problemscan exist with buried clay, ceramic, or concrete structures.Additionally, structures other than pipe can present similar concerns,such as for example non-metallic electrical conduit, irrigation tubing,fiberglass or other non-metallic underground storage tanks, septicsystem components, drainage structures, etc. Identifying the presenceand location of such structures can be important when trying to locatethe structures for repair or evaluation, or when digging or otherwisedisturbing the earth in the area, as when placing or building newstructures.

Various techniques have been proposed over the past 50 years foraddressing such problem. These have included placing of a coloredplastic sheet or tape over the pipe or other structure to provide avisible indicator of an underlying structure. A disadvantage of such asystem, however, is that the surrounding Earth must be disturbed tolocate the plastic sheet or tape.

In some prior art systems, a tape structure including a metal filmcombined with a colored polymer material has been utilized to provide avisual indicator of the material, if exposed, while enabling detectionof the metal. Such metal films are typically aluminum, copper, nickel,or a ferrous metal (or alloys of such materials). Conventional systemsutilizing such a conventional metal film tape do not provide suitabledetectable signature unless an electrical current is introduced throughthe metal film to establish a magnetic field that can then be detected.Introducing such an electrical current into a conventional marking tapecan be problematic, as it either requires access to one end of themetallized tape (for conductive locating) or electrical coupling betweenthe tape and the detector (for inductive locating). For the conductivelocating, the ability to detect the tape depends upon the tape remainingintact to maintain the conductive path.

In some systems, tags of various configurations have been proposed forattaching to non-metallic structures. One such tag that has beenproposed includes identifying information represented by patterns ofmagnetically permeable material (such as nanocrystalline or amorphousmetals or metal alloys), formed in the tag, and configured to be excitedby an alternating magnetic field of a selected frequency to provide anonlinear response including a detectable fundamental frequency andmultiple harmonic frequencies. The detector for interrogating such tagsis relatively complex, requiring phase difference detection between anemitting coil signal and a receiving coil signal. Such a system isdescribed in F. Belloir et. al, “A Smart Flat-Coil Eddy-Current Sensorfor Metal-Tag Recognition” Measurement Science & Technology; vol. 11,no. 4, pp. 367-374. In other systems, multiple receiving coils may beutilized. A Zitouni, et. al., “Pipe Identification by Optimized EddyCurrent Sensor” Additionally, such systems require matching of theexcitation signal with the characteristics of the coding of the tag(which may not always be known), and require emitting a signal withsufficient energy to saturate the tag to generate the characteristiceddy currents that may be detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example installation including an amorphous metal foilmarking tape in one contemplated application.

FIGS. 2A-2B each depict a respective example embodiment of an exampleamorphous metal foil marking tape.

FIGS. 3A-3C schematically depict respective contemplated applicationsincluding an amorphous metal tape, in which: FIG. 3A depicts amorphousmetal tape extending circumferentially around a non-metallic conduit atspaced intervals; FIG. 3B depicts amorphous metal tape extendingcircumferentially around and along a section of a non-metallic conduit;and FIG. 3C depicts an amorphous metal tape secured adjacent avertically-defined half-circumference of a non-metallic conduit.

FIGS. 4A-4C depict magnetostatic modeling of the distortion caused by apipe cross-section in the Earth's magnetic field, wherein: FIG. 4Adepicts distortion caused by a 4-inch iron pipe; FIG. 4B depictsdistortion caused by a 50 μm shell of cast-iron around a 4-inchnon-metallic pipe diameter; and FIG. 4C depicts distortion caused by a50 μm shell of an amorphous metal film around a 4-inch non-metallic pipediameter.

FIGS. 5A-5B depict alternative placements of an amorphous metal film incontemplated applications, in which: FIG. 5A depicts installation of anamorphous metal film in a generally horizontal orientation above anon-metallic conduit in a formed trench; and FIG. 5B depictsinstallation of an amorphous metal film in a generally verticalorientation above a non-metallic conduit in a plowed conduit recess.

FIG. 6 graphically depicts a comparison of detectable differentialmagnetic gradients of different conduit constructions as a function ofdepth.

FIG. 7 graphically depicts a comparison of detectable differentialmagnetic gradients of selected configurations of differentconfigurations of amorphous metal foil tape as a function of orientationand of depth.

FIG. 8 graphically depicts a comparison of detectable differentialmagnetic gradients of two different widths of amorphous metal foil tapeas a function of compass reference orientation (North-South, andEast-West).

FIG. 9 schematically depicts a vibratory plow suitable for achieving theinstallation depicted in FIG. 5B.

FIG. 10 depicts a comparison 1000 of the differential magnetic gradientof amorphous metal marking tapes of different configurations extendingin the North-South orientation.

FIG. 11 depicts trend lines of differential magnetic gradients resultingfrom an amorphous metal strip oriented in different positions relativeto the exterior of non-magnetic pipe.

DETAILED DESCRIPTION OF THE INVENTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Portions and features of some embodiments described herein may beincluded in, or substituted for, those of other embodiments.

The present description addresses methods and apparatus present foridentifying subterranean structures using amorphous metal markersassociated with the structures. In many examples, the amorphous metalmarker will include one or more sections of an amorphous metal foilwithin a protective enclosure sufficient to prevent contact betweensurrounding Earth and the amorphous metal foil, which could causecorrosion or other degradation of the amorphous metal foil.

The amorphous metal foil marker will be sized relative to the intendedinstallation to result in a localized variation in the Earth's magneticfield of a selected magnitude which can be detected. In many examples,such detection may be performed using a magnetic gradiometer. As will bedescribed below, in some examples the amorphous metal foil marker may beattached to the subterranean structure, while in other examples theamorphous metal foil marker may be placed proximate the subterraneanstructure (in many examples, directly above the subterranean structure).For purposes of the present description, the new amorphous metal markerswill be described in context of identifying the location of anon-metallic conduit, such as, for example as noted above, PVC orpolyethylene pipe or conduit, as identification of such non-metallicpipe has been a long-standing problem. Again as noted above, othernon-metallic structures (or merely non-magnetic structures) may beidentified in an analogous manner.

The term amorphous metal is used herein refers to metal alloy solidsthat lack a crystalline atom structure, and which include a “relativelyhigh magnetic relative permeability,” which in the context of thepresent description identifies a magnetic relative permeability between50,000 and 1,000,000. Such relatively high magnetic permeability may becompared, for example, to a magnetic relative permeability of copper(Cu) of about 1, and of iron (Fe) of about 5,000. Some amorphous metalalloys include either iron and/or cobalt (Co) in combination with Boron(B) and/or Silicon (Si). Though many other amorphous metal alloys withother compositions are known, amorphous metal alloys with thesecomponents offer high magnetic susceptibility.

The present description describes amorphous metal foil tapes extendingin “generally vertical” and “generally horizontal” orientations. Itshould be understood that the terms are used to described orientation ofa flexible tape in an Earth formation, and thus the terms are used as ageneral indication of orientation and not a suggestion of a specificangular orientation, or relative to the specific surface of the earthdirectly above a measurement location. As a result, the amorphous metalfoil marking tape is considered to extend “generally vertically” ifplane of the tape at a location in question lies at an angle within 45°to either direction of a vertical line relative to the generalizedcontours of the Earth's surface proximate the location of a portion ofthe tape in question; and similarly is considered to extend “generallyhorizontally” if the plane of the tape lies at an angle between 45° and135° relative to such a vertical line. As a specific example, referringto FIG. 5B, the figure depicts a segment of amorphous metal foil tape510 extending along an axis that is vertical (and generallyperpendicular) to the undisturbed Earth's surface indicated at 514 andnot with reference to the piled soil as indicated at 516.

Referring now to FIG. 1, the figure depicts an example installation 100including an amorphous metal marker, in the form of a tape 102, in oneintended application. Amorphous metal marker tape 102 is placed inspaced relation above a non-metallic pipe 104 within the Earth 106.Amorphous metal marker tape 102 is of a generally planar form, thoughflexible, and extends above at least a portion of the path of thenon-metallic pipe 104. In many installations, it will be desirable tohave such an amorphous metal marker tape extending for essentially theentire distance that a non-metallic pipe extends beneath the Earth'ssurface.

Located above the Earth's surface 108 is a detector 110. Detector 110may be selected from many types, including detectors for real timelocation operations, or, alternatively, other detecting systems having adetector to collect data (commonly correlated with GPS-derived locationinformation associated with the collected data) which will be processedsubsequently to identify the location of subterranean structures.

Though many types of detectors may be utilized with amorphous metalmarkers of the example configurations and characteristics as describedherein, a significant advantage of the described system is that, formany applications utilizing real time detection, a relatively simpledetector—a magnetic gradiometer—may be utilized instead of more complexand more expensive detectors. Because the described system measures alocalized change in the Earth's magnetic field resulting from presenceof the high magnetic permeability amorphous metal, the system does notrequire matching tuning between a frequency of a detector and afrequency response characteristic of the marker. As a result, thecurrently described systems are well suited for detection withoutspecialized knowledge of the marking system utilized. An examplemagnetic gradiometer suitable for use with systems as described hereinis the DML2000XRM model from Dunham & Morrow, Inc. of Kearneysville, W.Va. In general, such magnetic gradiometer use two (or more) spacedvector magnetic field sensors (such as fluxgate magnetometers) tomeasure anomalies along a selected axis. For many applications, amagnetic gradiometer capable of reading from 0 to 20 milliGauss (mG),with a resolution of 0.01 mG, or of generally comparable measurementcapabilities, will be suitable. With such a detector, the detectionthreshold for real time locating is approximately 1 to 2 mG.

More complex detectors may be used for real time detection of theamorphous metal marker tape so long as they are capable of identifyingthe localized distortion of the Earth's magnetic field, but such are notrequired. Additionally, to the extent desired for a specificapplication, either conductive or inductive detectors may be utilizedwith the described amorphous metal marker tape. As noted above, with aconductive detector, a current must be introduced into the amorphousmetal of the amorphous metal marker tape; while for an inductivedetector, an alternating signal will be used to induce a current intoamorphous metal of the amorphous metal marking tape, thereby generatinga magnetic field that may be detected. The amorphous metal marker isboth electrically conductive and has high magnetic permeability, whichallows it to be detected through conductive and inductive means.Furthermore, this combination of properties makes amorphous foil anideal target for inductive locating that can result in improvedsensitivity compared to conductive-only, non-ferrous markers such asaluminum.

In other applications, where data will be collected for subsequentprocessing, the detector may take measurements of variations in theEarth's magnetic field in an area of interest, preferably in correlationwith a GPS-based location sensor. Such detector systems are known topersons skilled in the art and may include movable land-based systems,such as handheld or wheeled detectors (either moved by hand or vehicles)interrogating the earth in the region of the detector, and associatingdetection data with GPS data and either recording the data in the unit,or transmitting the detection data and GPS data to a data repository. Inother examples, the detector may be airborne, such as carried by a planeor unmanned aerial vehicle (drone). The choice of the detectorconfiguration will often be based on the sum of the distances of alltraverses necessary to survey the area of interest; the necessarytraverses being a function of the width surveyed by each traverse andthe resolution required for the survey. In general, a ground-basedmagnetic field detector may be desirable for applications having a linesurvey of less than approximately 60 line-miles; a drone-based magneticfield detector may be desirable for applications requiring a survey upto approximately 1250 line miles; and a (manned) plane-based detectormay be desirable for applications requiring a survey over approximately1250 line miles. With such post-collection processing of magnetic fielddata, providing the capability of examining patterns in the data toidentify magnetic field distortions, it may be possible to reduce thedetection threshold, for example, to a range of 0.05 to 0.1 mG. As aresult, using such post-collection processing techniques effectivelyenabling a lower detection threshold, magnetic field distortions at agreater depth from the Earth's surface may be identified.

Referring now to FIGS. 2A-B, each figure depicts a respective exampleembodiment of an example amorphous metal foil marking tape that may beused, for example, in installation such as that described relative toFIG. 1. The term “amorphous metal foil marking tape,” will be utilizedto identify any of the various forms described herein which include anamorphous metal foil within some form of protective enclosure, asdescribed below. Thus, the term is applicable to the structures of FIGS.2A-B, as well as to those of any of FIGS. 3A-C.

FIG. 2A depicts a length of amorphous metal foil marking tape 200 havinga generally continuous layer of amorphous metal foil 202, encased withina protective enclosure 204. In many examples, the protective enclosurewill be formed of layers of polymer film laminated around the amorphousmetal foil 202. Additionally, in many examples the polymer film or othermaterials of the protective enclosure will be colored so as to be highlyvisible; and in some cases the color may be coded in accordance with thetype of conduit (or other structure) being marked. In some cases,textual information may be added to the colored laminate (or othermaterial forming some portion of the enclosure).

Different thicknesses of amorphous metal foil may be used such amorphousmetal foil marking tape 200, with foil of 0.001 inch thickness beingdetermined to be sufficient for many applications. In general, anamorphous metal foil having a thickness between approximately 0.0005inch and 0.002 inch will be desirable for use in the amorphous metalfoil marker tape. Amorphous metal foil 202 is described herein as agenerally continuous layer in view of it extending predominantly acrossthe entire length of a section of marking tape; but it should beunderstood that the amorphous metal foil 202 may be formed of differentsegments of amorphous metal foil placed sequentially with the end of onesegment near the end of another segment, but the different segments donot need to physically contact one another, as electrical conductivitythrough the amorphous metal foil is not required for the systemsdescribed herein. In this regard, amorphous metal foil marker tapehaving spaced segments of amorphous metal foil will not be suitable foruse with conductive detector systems, but may be used with inductivedetector systems.

FIG. 2B depicts an alternative configuration of an amorphous metal foilmarking tape 210, which includes multiple spaced segments of amorphousmetal foil 214 retained in spaced relation within an enclosure 212. Thechange from an essentially continuous amorphous metal foil layer, as inFIG. 2A, to a discontinuous layer with multiple segments represents atrade-off between utilizing less of the amorphous metal foil, but with aresulting tape that to some degree (depending on the space between thesegments), may cause less localized variation in the Earth's magneticfield, and may be more difficult to manufacture. However, as identifiedrelative to FIG. 8, a segmented amorphous metal foil tape may improveuniformity and consistent polarity of a detected response in somecircumstances.

In various examples, the amorphous metal foil marking tapes may be of adesired width across the generally planar surface extending orthogonalto the longitudinal axis of the tape, with widths between approximately4 inches and approximately 12 inches, being a useful dimension for manyapplications. In many examples, widths between approximately 5.5 inchesand 10 inches will be satisfactory for applications in which theamorphous metal foil marking tapes will be placed separate from, butextending in parallel relation to, an underlying non-metallic conduit(or other structure). As will be apparent to persons of skill in the arthaving the benefit of this disclosure, narrower tapes may be utilizedwhere the underlying non-metallic conduit will be relatively closer tothe Earth's surface (for example, within a foot or less, as may be thecase with electrical conduit or irrigation conduit, for example), ascompared to conduit that may be disposed more deeply, for example twofeet or more beneath the surface.

Another factor potentially influencing the choice of width of theamorphous metal foil marking tapes is the predominant compass directionof the conduit path to be marked. As addressed later herein in referenceto FIG. 8, described systems using amorphous metal foil marking tapesresult in greater localized disturbance of the Earth's magnetic fieldwhen extending in a generally North-South direction, as compared to whenextending in an East-West direction. As a result, in marking conduits(or portions thereof) extending predominately in an East-West directionit may be advantageous to use an amorphous metal foil marking tape of anincreased dimension to present a similar detectable signal to that seenrelative to marking tape extending in a generally North-South direction.

The laminated enclosures for either of amorphous metal foil marking tape200 or 210 may be of any polymer suitable for providing strength andabrasion resistance sufficient to facilitate handling and placing of thetape, while protecting the tape from exposure to the surrounding Earthand elements when installed. For example, two layers of polyethylene,ranging between 0.002 and 0.004 inches in thickness has been foundsuitable.

The amorphous metal foil used in the systems described herein can be ofmany types known to persons skilled in the art. Tests have beenperformed with several amorphous foil alloys available from MetglasInc., of Conway, S.C., using both iron and cobalt-based metallurgies,with characteristics as set forth below in Table 1:

Relative Induction, T at an Magnetic Alloy Applied Field of 800 A/mPermeability Composition 2605CO 1.15 156,400 Fe—Co—B 2605HB1M 0.958159,900 Fe—B—Si 2605SA1 0.829 67,890 Fe—B—Si 2705M 0.754 929,300 Co—B—Si2714A 0.602 190,000 Co—B—Si

The above characteristics are based in the on the metal foil in anas-cast state (i.e. without a secondary annealing cycle). Based uponcomparisons of the detectability of sample structures with each of theidentified alloys, each of the above alloys provided similardetectability. Although a secondary annealing cycle can result inincreased brittleness of the amorphous metal foil separations that mightimpact the electrical conductivity through the amorphous metal foil,such breaks electrical conductivity are not of concern for the presentlydescribed systems.

Referring now also to FIG. 6, the figure graphically depicts acomparison 600 of detectable differential magnetic gradients of two ofthe above amorphous metal foils to a steel pipe, each as a function ofdistance to the detecting gradiometer. Trend line 602 generallyrepresents a 4-inch National Pipe Thread (NPT) steel pipe, while trendline 604 generally represents a 4-inch non-metallic pipe wrapped withthe identified 2605HB1M Fe—B—Si alloy; and trend line 606 generallyrepresents a 4-inch non-metallic pipe wrapped with the identified 2705MCo—B—Si alloy. Notwithstanding the generally higher magneticpermeability of the 2705 alloy over that of the 2605HB1M alloy (929,300to 159,900), there was minimal difference in detectability.

In other example systems, the amorphous metal foil marking tape may besecured to the conduit (or other structure). Referring now to FIGS.3A-C, each represents an example configuration in which an amorphousmetal foil marking tape is applied to an example conduit. FIG. 3Adepicts an example configuration 300 in which multiple segments ofamorphous metal foil marking tape 302 each extend circumferentiallyaround a non-metallic conduit 304 at spaced intervals. The relativethickness of the amorphous metal foil marking tape is exaggerated in thefigure for purposes of illustration. As shown in the insetcross-section, in the depicted example, the segments of amorphous metalfoil marking tape 302 extend completely around the circumference ofconduit 304. In some examples, the circumferential bands of each markingtape segment 302, may extend, for example, between approximately 8inches and approximately 2 feet along conduit 304

In example configuration 300, the circumferential segments of amorphousmetal foil tape are essentially evenly spaced along the depicted lengthof conduit 304. In other applications, the circumferential segments ofamorphous metal foil marking tape may be unevenly spaced, so as toprovide a directional indication that may be easily detected. Forexample, as just one example of such a system, a system may include two(or more) include segments of amorphous metal foil marking tape inrelatively closely spaced relation with one another (for example within1 to 1.5 feet of one another), and with the next pair (or group) ofsegments spaced approximately 6 to 10 feet away

An advantage of example systems utilizing bands of the amorphous metalfoil marking tape extending circumferentially around a conduit resultfrom the relatively large impact of the structure on the Earth'sgravitational field. Referring now also to FIGS. 4A-C, those figuresdepict comparative magnetostatic modeling of the distortion caused by apipe cross-section in the Earth's magnetic field, in which: FIG. 4Adepicts modeled distortion resulting from a 4-inch iron pipe; FIG. 4Bdepicts distortion resulting from a 50 μm shell of cast-iron around a4-inch non-metallic pipe diameter; and FIG. 4C depicts distortionresulting from a 50 μm shell of an amorphous metal film around a 4-inchnon-metallic pipe diameter.

As can be seen from a comparison of FIG. 4C to FIG. 4A, the 50 μmamorphous metal film provide a generally equivalent distortion of theEarth's magnetic field to that provided by a comparably sized cast-ironpipe. Additionally, the distortion is much greater than that provided bya 50 μm cast-iron sleeve due to the substantially greater magneticpermeability of the amorphous metal, 80,000 versus 4,000 (typicalpermeability values that were used in the modeling). However, it shouldbe noted that for smaller size structures, for example three-quarterinch or 1 inch diameter polyethylene or PVC pipe or tubing, thedimensions of a circumferential band of amorphous metal foil may notcreate sufficient distortion of the Earth's magnetic field to facilitatereliable detection, and therefore use of an amorphous metal foil markingtape separate from the pipe structure may be desirable for suchapplications.

Referring now to FIG. 3B, the figure depicts an embodiment 310 in whichamorphous metal tape 312 extends circumferentially around andcontinually along a section of a non-metallic conduit 314. Assuming thenon-metallic conduit 314 is of sufficient diameter, as can be seen fromthe modeling of FIGS. 4A-C, the wrapping of the amorphous metal tape maymore closely approximate the signature of an iron pipe; however, such anapproach utilizes a relatively maximum volume of amorphous metal foiltape.

As an alternative approach, FIG. 3C depicts an alternative configuration320 in which an amorphous metal foil marking tape 322 is securedadjacent a vertically defined half-circumference of a non-metallicconduit 324. As discussed in more detail in reference to FIG. 7,evaluation performed to this point suggests that relatively greaterdisruption of the Earth's magnetic field results from generally verticalplanar structures (i.e. planar structures extending generallyvertically), in contrast, for example, to generally horizontallyextending planar structures.

In circumstances in which the amorphous metal foil marking tape assumesa more vertically curvilinear form, as in FIG. 3C, it appears thatgreater disruption of the Earth's magnetic field results fromorientations of the amorphous metal foil that provide the greatestvertical dimension. For example, the configuration 320 is believed toprovide greater disruption of the Earth's magnetic field than would beprovided by an embodiment with amorphous metal foil tape extending overa different half circumference of conduit 324 (for example, a halfcircumference radially offset by 90° from that depicted in FIG. 3C), andthereby having a lesser vertical dimension.

The impact of the orientation of a curvilinear section of amorphousmetal foil is depicted in FIG. 11. The figure depicts trend lines of thedifferential magnetic gradient resulting from a 1-inch wide striporiented in different positions relative to the exterior of a 1-inch PVCpipe. In a first orientation 1102, in which the tape is arranged toprovide the greatest vertical dimension, the corresponding trend line1104 indicates the greatest differential gradient. In orientation 1106,trend line 1108 depicts a reduced gradient; and orientation 1110,offering the minimal vertical dimension, results in trend line 1112,defining a further reduced magnetic gradient.

Referring now to FIGS. 5A-B, the figures depict alternative placementsof an amorphous metal film in contemplated applications, in which FIG.5A depicts installation 500 of an amorphous metal marker tape 502 in agenerally horizontal orientation above a non-metallic conduit 506 in aformed (and filled) trench 504 in the Earth 508; and FIG. 5B depictsinstallation of an amorphous metal marker tape 510 in a generallyvertical orientation above a non-metallic conduit 512 in a plowedrecess. As noted above, the horizontal orientation will result in lesslocalized change in the Earth's magnetic field to facilitate detection,but may be adequate for many applications particularly depending uponthe presence (or absence) of sources of background disruptions, thedepth of the tape, etc. A trench 504 as depicted may be formed byconventional trench digging devices.

Vibratory and static plows are used with conventional marking tapes toopen a furrow, and to subsequently simultaneously feed a PVC conduitinto the furrow, while allowing the conventional marking tapes to feedinto the furrow above the conduit. With such conventional marking tapes,the orientation of the marking tapes is of little significance sincethey are merely intended to provide a visual warning once digging isunderway. As discussed in more detail relative to FIG. 9, a plowstructure is contemplated which facilitates feeding an amorphous metalfoil marking tape into a furrow in a generally vertical orientation, asdepicted in FIG. 5B. Due to the tendency of the furrow to close onitself after passage of the plow blade, maintaining generally verticalorientation of the amorphous metal foil marking tape may be easier in aplowed furrow.

FIG. 7 graphically depicts a comparison 700 of detectable differentialmagnetic gradients of selected configurations of differentconfigurations of amorphous metal foil marking tape (each having a stripof amorphous metal foil with a width of 6 inches) as a function oforientation and of distance from a detecting gradiometer. Trend line 702generally represents the magnetic gradient of a 36 inch length of theamorphous metal foil marking tape when placed in a vertical orientation(generally as depicted in FIG. 5B); while trend line 704 represents themagnetic gradient of a 36 inch length of the same dimension of amorphousmetal foil marking tape when placed in a horizontal orientation(generally as depicted in FIG. 5A). Trend line 706 represents themagnetic gradient of a 12-inch long vertical strip when placed in avertical orientation; as compared to trend line 708 representing themagnetic gradient of the 12-inch long vertical strip placed in ahorizontal orientation. As indicated by comparison 700, with otherfactors being consistent, use of longer segments of amorphous metal foilimproves detectability over relatively shorter segments; and placingsegments of amorphous metal foil in a generally vertical orientationimproves detectability over foil in a generally horizontal orientation.

As noted previously, the orientation of a length of amorphous metal foilmarking tape relative to the magnetic north-south axis affects the peakmagnetic distortion resulting from the tape, and thus the detectabilityof the tape. Referring now to FIG. 8, the figure graphically depicts acomparison 800 of two different widths of amorphous metal foil markingtape (all strips 36 inches long, and each oriented vertically) as afunction of compass reference orientation (North-South, and East-West).Curve 802 depicts the differential magnetic gradient of a 10-inch wideamorphous metal foil strip disposed along a North-South axis; whilecurve 804 depicts the differential magnetic gradient of an 8-inch wideamorphous metal foil strip disposed along a North-South axis. Incontrast, curve 806 depicts a 10-inch wide amorphous metal foil stripdisposed along an East-West axis, while curve 808 depicts an 8-inch wideamorphous metal strip disposed along an East-West axis. As can be seenfrom comparison 800 the peak differences in the differential magneticgradient between the two different widths of amorphous metal stripsdiffered from one another by approximately 17% in the North-Southorientation, but differed from one another by approximately 32% in theEast-West orientation. Additionally, the peak differences in thedifferential magnetic gradient between similar width strips differed byapproximately 35% for the 10 inch widths oriented North-South versusEast-West, but by approximately 47% for the same comparison of 8 inchwidths. As a result, some example installations may benefit from use ofa greater dimension (i.e., width) of amorphous metal foil marking tapewhen extending in a compass orientation closer to an East-Westorientation than to a North-South orientation (i.e., extending along anaxis within a range between a NW-SE axis, and a SW-NE axis).

An evaluation of different configurations of amorphous metal foilmarking tape have identified that use of a marking tape having spacedsegments of amorphous metal foil in linearly spaced relation to oneanother, as in FIG. 2B, can eliminate the variation in signal strengthand polarity associated with a solid amorphous metal foil marking tape(e.g. FIG. 2A) oriented North-South as reflected in FIG. 8, at curves802 and 804 at 810 and 812. Referring now also to FIG. 10, the figuredepicts a comparison 1000 of the differential magnetic gradient ofamorphous metal marking tapes extending in the North-South orientation,comparing a continuous foil tape represented by curve 1002, to asegmented foil tape (one foot lengths of amorphous metal foil spaced atone foot intervals), represented by curve 1004.

FIG. 9 schematically depicts a plow 900 suitable for achieving theinstallation depicted in FIG. 5B. Plow 900 is configured for movement bya tractor or similar vehicle, and includes a plow blade 902 configuredto create a furrow through longitudinal movement; and in some examplesmay also incorporate vibratory energy (such as may be created through apower take off (PTO) vibrating mechanism in a support assembly coupledto plow 900). Plow 900 includes a conduit feed passage, indicatedgenerally at 920, for receiving a flexible conduit through an upperportion of the plow, as indicated at 906A, and feeding the conduit to anexit 908 at the back of the plow blade 902 allowing the conduit to beplaced toward a lower portion of the formed furrow, as indicated at906B. Plow 900 also includes a marking tape feed path, indicatedgenerally at 914, which receives a feed supply of marking tape asindicated at 910A and allows the marking tape to be fed to an exitindicated generally at 912 to be placed in the furrow at a verticallyspaced position above conduit 906B, as indicated at 910B. Unlikeconventional plow conduit placement systems, plow 900 includes a feedpath 914 configured to turn the marking tape at a roller or guideassembly, indicated schematically at 916, to place the tape in thevertical orientation, identified as the preferable orientation, asdiscussed above. In some example systems the marking tape may becontained in a spool mounted on the plow, as indicated at 918; oranother systems the marking tape may be on a spool at another location,for example mounted on a conveying tractor coupled to plow 900. In somesuch embodiments, an orienting roller to receive and guide the tape intothe plow may be used instead of spool 918.

To better illustrate the methods and apparatuses described herein, anon-limiting set of example embodiments are set forth below asnumerically identified examples:

Example 1 is a subterranean installation, comprising: a non-metallicstructure covered by some dimension of Earth, hiding the location of thestructure; and a marking tape disposed in proximity to the non-metallicstructure, the marking tape comprising, an amorphous metal foil layer,and a protective covering preventing direct contact between theamorphous metal foil layer and the surrounding Earth.

In Example 2, the subject matter of Example 1 wherein the non-metallicstructure comprises PVC pipe.

In Example 3, the subject matter of any one or more of Examples 1-2wherein the marking tape is attached to the non-metallic structure.

In Example 4, the subject matter of any one or more of Examples 1-3wherein the marking tape extends in the direction of the non-metallicstructure and in spaced relation above the non-metallic structure.

In Example 5, the subject matter of any one or more of Examples 1-4wherein the non-metallic structure is a non-metallic pipe, and whereinmultiple pieces of marking tape are arranged in spaced relation to oneanother a long at least a portion of the non-metallic pipe.

In Example 6, the subject matter of any one or more of Examples 1-5wherein the multiple pieces of marking tape extend around at least aportion of the circumference of the non-metallic pipe.

In Example 7, the subject matter of any one or more of Examples 1-6wherein the protective covering comprises a polymer film laminatedaround the amorphous metal foil layer.

In Example 8, the subject matter of any one or more of Examples 1-7wherein the protective covering comprises a polyethylene film.

In Example 9, the subject matter of any one or more of Examples 7-8wherein the protective covering includes a colored material for improvedvisibility.

In Example 10, the subject matter of any one or more of Examples 1-9wherein the amorphous metal foil has a magnetic relative permeabilitygreater than 50,000.

In Example 11, the subject matter of any one or more of Examples 1-10wherein the amorphous metal foil comprises an alloy including at leastone of iron (Fe) and cobalt (Co).

In Example 12, the subject matter of any one or more of Examples 1-11wherein the amorphous metal foil has a thickness between 0.0005 inch and0.002 inch.

Example 13 is a method of forming a subterranean installation,comprising: placing a non-metallic structure within a recess within theEarth; and placing a marking tape in proximity to the non-metallicstructure, the marking tape comprising, an amorphous metal foil layer,and a protective covering preventing direct contact between theamorphous metal foil layer and the surrounding Earth.

In Example 14, the subject matter of Example 13 wherein the non-metallicstructure comprises PVC pipe.

In Example 15, the subject matter of any one or more of Examples 13-14wherein placing a marking tape in proximity to the non-metallicstructure comprises attaching the marking tape to the non-metallicstructure.

In Example 16, the subject matter of any one or more of Examples 13-15wherein placing a marking tape in proximity to the non-metallicstructure comprises placing the marking tape in spaced relation abovethe non-metallic structure.

In Example 17, the subject matter of any one or more of Examples 13-16wherein the non-metallic structure is a non-metallic pipe, and whereinmultiple pieces of marking tape are arranged in spaced relation to oneanother a long at least a portion of the non-metallic pipe.

In Example 18, the subject matter of Example 17 wherein the amorphousmetal is contained within a continuous section of amorphous metalmarking tape, wherein the marking tape comprises a section with multipleamorphous metal foil pieces arranged in linearly spaced relation to oneanother along the portion of the non-metallic pipe.

In Example 19, the subject matter of any one or more of Examples 13-18wherein the multiple pieces of marking tape extend around at least aportion of the circumference of the non-metallic pipe.

In Example 20, the subject matter of any one or more of Examples 13-19wherein the protective covering comprises a polymer film laminatedaround the amorphous metal foil layer.

In Example 21, the subject matter of Example 20 wherein the polymer filmcomprises a polyethylene film.

In Example 22, the subject matter of any one or more of Examples 13-21wherein the amorphous metal foil has a magnetic relative permeability of50,000 or greater.

Example 23 is a method of identifying the location of an undergroundnon-metallic conduit, comprising: measuring a localized variation in theEarth's magnetic field through use of a magnetic gradiometer; andwherein the localized variation in the Earth's magnetic field is causedby an amorphous metal foil marker placed proximate at least a portion ofthe underground non-metallic conduit, wherein the amorphous metal foilmarker includes an area of amorphous metal foil sufficient to establisha selected degree of localized variation in the Earth's magnetic field,the amorphous metal foil retained within protective enclosure.

In Example 24, the subject matter of Example 23 wherein the amorphousmetal foil marker is configured to establish the localized variation inthe Earth's magnetic field in the absence of any introduction of currentto the metal foil.

In Example 25, the subject matter of any one or more of Examples 23-24wherein the amorphous metal foil marker is attached to the non-metallicconduit.

In Example 26, the subject matter of Example 25 wherein the amorphousmetal foil marker extends around at least a portion of a transversecross-section through the non-metallic conduit.

In Example 27, the subject matter of any one or more of Examples 23-26wherein the amorphous metal foil marker is placed above the at least aportion of the underground non-metallic conduit and extending along thepath of the conduit.

In Example 28, the subject matter of Example 27 wherein the amorphousmetal foil marker is a generally flat structure, with the widthextending generally vertically relative to the Earth's surface.

In Example 29, the subject matter of any one or more of Examples 27-28wherein the measuring a localized variation in the Earth's magneticfield is performed to identify the localized variation in real time.

In Example 30, the subject matter of any one or more of Examples 27-29wherein measuring a localized variation in the Earth's magnetic fieldcomprises: collecting magnetic field strength data correlated with GPSpositioning data; and after collection of the magnetic field strengthdata and GPS data, analyzing the data to identify field strengthvariations consistent with an amorphous metal foil marker.

In Example 31, the subject matter of Example 30 wherein collectingmagnetic field strength data correlated with GPS positioning data isperformed through use of a hand-held detector.

In Example 32, the subject matter of any one or more of Examples 30-31wherein collecting magnetic field strength data correlated with GPSpositioning data is performed through use of a wheeled detector movableacross the Earth's surface.

In Example 33, the subject matter of any one or more of Examples 30-32wherein collecting magnetic field strength data correlated with GPSpositioning data is performed through use of an airborne detector.

In Example 34, the subject matter of any one or more of Examples 30-33wherein the airborne detector is supported by an unmanned aerialvehicle.

In Example 35, the subject matter of any one or more of Examples 30-34wherein the airborne detector is supported by an airplane.

In Example 36, wherein the method of any one or more of Examples 23-35are performed on a subterranean installation in accordance with any ofExamples 1-12.

In Example 37, wherein the method of forming a subterranean installationof any of Examples 13-22, is used to produce a subterranean installationin accordance with any of Examples 1-12.

In Example 38, wherein the method of any one or more of Examples 23-35are performed on a subterranean installation formed in accordance withany one or more of Examples 13-22.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. In addition, in the above DetailedDescription, various features have been grouped together to streamlinethe disclosure. This should not be interpreted as intending that anunclaimed disclosed feature is essential to any claim. Rather, inventivesubject matter may lie in less than all features of a particulardisclosed embodiment. Thus, the following claims are hereby incorporatedinto the Detailed Description, with each claim standing on its own as aseparate embodiment, and it is contemplated that such embodiments can becombined with each other in various combinations or permutations. Thescope of the invention should be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

What is claimed is:
 1. A subterranean installation, comprising: anon-metallic structure covered by some dimension of Earth, hiding thelocation of the structure; and a marking tape disposed in proximity tothe non-metallic structure, the marking tape comprising, an amorphousmetal foil layer, and a protective covering preventing direct contactbetween the amorphous metal foil layer and the surrounding Earth.
 2. Thesubterranean installation of claim 1, wherein the non-metallic structurecomprises PVC pipe.
 3. The subterranean installation of claim 1, whereinthe marking tape is attached to the non-metallic structure.
 4. Thesubterranean installation of claim 1, wherein the marking tape extendsin the direction of the non-metallic structure and in spaced relationabove the non-metallic structure.
 5. The subterranean installation ofclaim 1, wherein the non-metallic structure is a non-metallic pipe, andwherein multiple pieces of marking tape are arranged in spaced relationto one another a long at least a portion of the non-metallic pipe. 6.The subterranean installation of claim 1, wherein the multiple pieces ofmarking tape extend around at least a portion of the circumference ofthe non-metallic pipe.
 7. The subterranean installation of claim 1,wherein the protective covering comprises a polymer film laminatedaround the amorphous metal foil layer.
 8. The subterranean installationof claim 1, wherein the protective covering comprises a polyethylenefilm.
 9. The subterranean installation of claim 7, wherein theprotective covering includes a colored material for improved visibility.10. The subterranean installation of claim 1, wherein the amorphousmetal foil has a magnetic relative permeability greater than 50,000. 11.The subterranean installation of claim 1 or in the amorphous metal foilcomprises an alloy including at least one of iron (Fe) and cobalt (Co).12. The subterranean installation of claim 1, wherein the amorphousmetal foil has a thickness between 0.0005 inch and 0.002 inch.
 13. Amethod of forming a subterranean installation, comprising: placing anon-metallic structure within a recess within the Earth; and placing amarking tape in proximity to the non-metallic structure, the markingtape comprising, an amorphous metal foil layer, and a protectivecovering preventing direct contact between the amorphous metal foillayer and the surrounding Earth.
 14. The method of forming asubterranean installation of claim 13, wherein the non-metallicstructure comprises PVC pipe.
 15. The method of forming a subterraneaninstallation of claim 13, wherein placing a marking tape in proximity tothe non-metallic structure comprises attaching the marking tape to thenon-metallic structure.
 16. The method of forming a subterraneaninstallation of claim 13, wherein placing a marking tape in proximity tothe non-metallic structure comprises placing the marking tape in spacedrelation above the non-metallic structure.
 17. The method of forming asubterranean installation of claim 13, wherein the non-metallicstructure is a non-metallic pipe, and wherein multiple pieces ofamorphous metal are arranged in spaced relation to one another along atleast a portion of the non-metallic pipe.
 18. The method of forming asubterranean installation of claim 17, wherein the amorphous metal iscontained within a continuous section of amorphous metal marking tape,wherein the marking tape comprises a section with multiple amorphousmetal foil pieces arranged in linearly spaced relation to one anotheralong the portion of the non-metallic pipe.
 19. The method of forming asubterranean installation of claim 13, wherein the multiple pieces ofmarking tape extend around at least a portion of the circumference ofthe non-metallic pipe.
 20. The method of forming a subterraneaninstallation of claim 13, wherein the protective covering comprises apolymer film laminated around the amorphous metal foil layer.
 21. Themethod of claim 20, wherein the polymer film comprises a polyethylenefilm.
 22. A method of identifying the location of an undergroundnon-metallic conduit, comprising: measuring a localized variation in theEarth's magnetic field through use of a magnetic gradiometer; andwherein the localized variation in the Earth's magnetic field is causedby an amorphous metal foil marker placed proximate at least a portion ofthe underground non-metallic conduit, wherein the amorphous metal foilmarker includes an area of amorphous metal foil sufficient to establisha selected degree of localized variation in the Earth's magnetic field,the amorphous metal foil retained within protective enclosure.
 23. Themethod of claim 22, wherein the amorphous metal foil marker isconfigured to establish the localized variation in the Earth's magneticfield in the absence of any introduction of current to the metal foil.24. The method of claim 22, wherein the amorphous metal foil marker isattached to the non-metallic conduit.
 25. The method of claim 24,wherein the amorphous metal foil marker extends around at least aportion of a transverse cross-section through the non-metallic conduit.